1. Field of the Invention
The present invention pertains to a method for carrying out a plastic-working on an ingot of a boron-containing heat-resistant alloy without reducing its boron content.
2. Prior Art
It has hitherto been known that boron-containing heat-resistant nickel-based alloys or cobalt-based alloys have strength at high temperatures and superior resistance to oxidation, and that the boron contained therein particularly contributes to improve high-temperature creep characteristics. A typical nickel-based alloy of the aforesaid kind is disclosed in Japanese Patent Publication No. 55-9940, and it contains at least one element selected from the group consisting of 0.04% to 0.25% by weight of carbon (C), 20.0% to 25.0% by weight of chromium (Cr), 16.0% to 20.0% by weight of iron (Fe), 8.0% to 10.0% by weight of molybdenum (Mo), 0.2% to 1.0% by weight of tungsten (W), 0.4% to 1.5% by weight of manganese (Mn), 0.05% to 0.5% by weight of silicon (Si), no greater than 0.02% by weight of boron (B), no greater than 0.1% by weight of aluminum (Al), no greater than 0.02% by weight of titanium (Ti), no greater than 0.6% by weight of cobalt (Co), no greater than 0.05% by weight of zirconium (Zr), no greater than 0.02% by weight of calcium (Ca), and no greater than 0.02% by weight of rare earth metals; balance nickel and unavoidable impurities. Another nickel-based alloy is the one having AMS standard 5536H, which contains 0.05% to 0.15% by weight of carbon, 20.5% to 23.0% by weight of chromium, 17.0% to 20.0% by weight of iron, 8.0% to 10.0% by weight of molybdenum, 0.2% to 1.0% by weight of tungsten, no greater than 1% by weight of manganese, no greater than 1% by weight of silicon, no greater than 0.01% by weight of boron, no greater than 0.5% by weight of aluminum, no greater than 0.15% by weight of titanium, 0.5% to 2.5% by weight of cobalt, no greater than 0.05% by weight of copper (Cu), no greater than 0.04% by weight of phosphorus (P), no greater than 0.03% by weight of sulfur (S), balance nickel and unavoidable impurities. And yet another nickel-based alloy contains 0.08% by weight of carbon, 21% by weight of chromium, 9.0% by weight of molybdenum, 0.003% by weight of tungsten, 0.5% by weight of aluminum, 0.3% by weight of titanium, 12% by weight of cobalt, balance nickel and unavoidable impurities.
When a plastic-working, such as breakdown-forging, hot rolling and cold drawing, is carried out on the nickel-based alloys described above or on other boron-containing heat-resistant alloys, the boron content is substantially decreased. The decrease is particularly severe at a portion adjacent to the surface of the alloy. Therefore, when manufacturing fine wire members, thin plates or tubes with thin walls from ingots of the above boron-containing alloys, the decrease of the boron content becomes crucial, so that the products having a desired boron content and hence desired mechanical characteristics such as high-temperature creep characteristics cannot be obtained.